Cushioned bumper for scrapers

ABSTRACT

A cushioned bumper for ground scrapers comprising a housing adapted to be mounted on the rear end of the scraper in a generally horizontal postion and extending longitudinally of the scraper, with the housing carrying a pair of internal stop elements, a tubular plunger structure reciprocably mounted in the housing and carrying stop lugs, adapted to engage the respective housing stop elements, and a buffer plate exposed exteriorly of the housing against which the blade of a bulldozer or the like will engage to push the scraper when struck, and a composite cushioning arrangement interposed between the housing and the plunger including spring means to bias the plunger structure outwardly against the housing stop elements, in which the sides of the housing are equipped with special stiffener elements that hold the housing stop elements and the housing side walls bearing same against displacement laterally outwardly of the housing due to recoil and the lateral forces due to the bulldozer working against the plunger in rough terrain.

United States Patent [1 1 Kanjo [451 Sept. 17, 1974 CUSHIONED BUMPER FOR SCRAPERS Wajih Kanjo, Midlothian, Ill.

[73] Assignee: Cardwell Westinghouse Company,

Chicago, Ill.

[22] Filed: Oct. 25, 1973 [21] Appl. No.: 409,579

[75] Inventor:

[52] US. Cl 280/481, 293/60, 293/DIG. 1

[51] Int. Cl. B60! 19/08, B60d 3/00 [58] Field of Search 280/481; 293/60, 85, 86,

293/88, DIG. l, DIG. 2, BIG 5; 267/116, 140; 213/223 [56] References Cited UNITED STATES PATENTS 3,214,192 10/1965 Hamm 280/481 3,785,679 1/1974 Peterson et al. 267/140 Primary ExaminerM. Henson Wood, Jr.

Assistant ExaminerRobert Saifer Attorney, Agent, or FirmMann, Brown, McWilliams & Bradway [5 7 ABSTRACT A cushioned bumper for ground scrapers comprising a housing adapted to be mounted on the rear end of the scraper in a generally horizontal postion and extending longitudinally of the scraper, with the housing carrying a pair of internal stop elements, a tubular plunger structure reciprocably mounted in the housing and carrying stop lugs, adapted to engage the respective housing stop elements, and a buffer plate exposed exteriorly of the housing against which the blade of a bulldozer or the like will engage to push the scraper when struck, and a composite cushioning arrangement interposed between the housing and the plunger including spring means to bias the plunger structure outwardly against the housing stop elements, in which the sides of the housing are equipped with special stiffener elements that hold the housing stop elements and the housing side walls bearing same against displacement laterally outwardly of the housing due to recoil and the lateral forces due to the bulldozer working against the plunger in rough terrain.

8 Claims, 4 Drawing Figures PATENIED SEP I 7 I974 sum 1 or 2 FI G. 2

CUSHIONED BUMPER FOR SCRAPERS This invention relates to a cushioned bumper for scrapers, and more particularly to a cushioned scraper bumper adapted for application to the rear end of earth moving scrapers to cushion the shock involved when the scraper is bumped from the rear to start it when struck. Specifically, this invention is concerned with improvements in the cushioned scraper bumper disclosed in Bertil E. Peterson Patent application Ser. No. 242,329, filed Apr. 10, 1972 now US. Pat. No. 3,785,679 (and assigned to assignee of the present application).

Scrapers are familiar pieces of earth moving equipment which take on a load by moving the scraper over earth to be moved, with the scraping blade lowered to take on the load of earth, and when loaded, the scraper is moved to another location where the scraper load is discharged in a conventional manner. Scrapers being large and heavy pieces of equipment, and being used primarily to handle relatively soft earth, they frequently become stuck during the process of being loaded and moved to the point of earth disposal. As equipment of this type may weigh on the order of 50,000 pounds, and carry a 50,000 pound load, it is quite a problem to get them started moving once they have stalled.

The practice has developed in the industry of using a bulldozer to get a stuck or mired scraper moving, and this is accomplished by moving the bulldozer against the rear end of the scraper (which is equipped with a fixed bumper for that purpose) so that the power provided by the scraper can be applied to the scraper to get the scraper moving. Of course, it would be preferable to be able to run the bulldozer against the rear end of the scraper at low but controlled speed, but the resulting impact would create quite a whiplash problem for the operators, and overstress the equipment involved. Operators for their own safety have come to require that the bulldozer start up from a full stop, after the bulldozer blade is carefully brought against the scraper bumper, to minimize the whiplash problem. This, of course, wastes time and requires a lot more power and fuel than if the bulldozer could run into the scraper bumper while moving.

In accordance with the invention of said Peterson application, a cushioned scraper bumper is provided comprising a housing adapted to be mounted on the rear end of the scraper in a generally horizontal position and extending longitudinally of the scraper, a tubular plunger structure reciprocably mounted in the housing and carrying a bumper plate exposed exteriorly of the housing against which the plate of a bulldozer or the like impacts to push the scraper when stalled, and a composite cushioning arrangement interposed between the housing and the plunger including a pressure responsive variable orifice type hydraulic cushioning unit and one or more resilient pad type cushioning units that absorb the impetus of the dynamic forces applied to the scraper by the bulldozer. The hydraulic cushioning unit provides a hydraulic cushioning action for the full stroke of the unit in a manner which allows for the scraper engaging against fixed obstructions such as boulders or the like, with the resilient cushioning units coming into operation at approximately the threequarter point of the closure stroke to act in parallel with the hydraulic unit in absorbing the impetus of the pushing forces involved. The result is that the scraper when stalled can be pushed into motion when fully loaded by impacting the bulldozer into the scraper at speeds on the order of l to 2 miles per hour while not exposing the vehicle operators to whiplash problems or overstressing the equipment. Similarly, if the scraper in being pushed strikes immovable objects such as boulders or the like, the hydraulic cushioning device acts to fully cushion the resulting shock without overstressing the cushioning mechanism or the vehicles and without causing distress to the operator.

The scraper bumper of said application includes a special mounting arrangement for the housing stop lugs (against which the plunger stop lugs engage on the return stroke of the plunger) in accordance with which the housing stop lugs are carried by removably mounting plates that are bolted to the housing side walls to dispose the housing stop lugs in their operative positions.

The present invention is concerned with improvements in the cushioned bumper of said Peterson application with reference to the arrangement of the housing stop lugs and reinforcement of same against stresses imposed by recoil of the plunger structure.

A principal object of this invention is to provide a bracing and holding arrangement for the bumper mounting stop lug mounting plates that takes the recoil shocks which are applied to the housing stop lugs, instead of having such shocks resisted by the bolts which secure the lug mounting plates to the housing.

Other important objects of the invention are to generally improve the mounting arrangement of the lug mounting plates, and housing, and provide a cushioned bumper arrangement that is economical of manufacture, convenient to install, and long lived in operation.

In accordance with this invention, the bumper housing has applied to either side of same, externally of the respective housing side walls. special stiffener elements that receive the respective housing lug mounting plates between them and the respective housing side walls and hold the respective housing stop lugs and mounting plates against displacement laterally outwardly of the housing due to recoil. The mounting plates are each equipped with an externally disposed stop lug that is in abutting relation with the rspective stiffener elements whereby the shocks due to recoil are borne by the respective stiffener elements rather than the mounting plate bolts.

Still other objects, uses, and advantages will be obvious or become apparent from a consideration of the following detailed description and the application drawings.-

In the drawings:

FIG. 1 is a diagrammatic perspective view of the rear end of a typical scraper, showing a cushioned bumper applied thereto that is in accordance with the present invention;

FIG. 2 is a side elevational view of the scraper bumper, with parts broken away;

FIG. 3 is a plan view of the cushioning device shown in FIG. 2, with parts shown in section; and

FIG. 4 is an end view of the device shown in FIG. 3, taken from the right hand side of FIG. 3.

However, it is to be understood that the specific drawing illustrations provided are supplied primarily to comply with requirements of the Patent Laws, and that the invention is susceptible of other embodiments that will be obvious to those skilled in the art, and which are intended to be covered by the appended claims.

GENERAL DESCRIPTION Reference numeral of FIG. 1 genrally indicates a cushioned scraper bumper arranged in accordance with this invention applied to the rear end 12 of an earth moving scraper 14 for purposes of starting the scraper 14 when stalled by using a bulldozer or the like piece of equipment. The scraper 14 is not shown except for its rear end 12, and it may be any one of a number of conventional makes well known to the art. Examples are the B3 39F tractor scraper made by The Construction Equipment Division of Westinghouse Air Brake Company and the TS-24 Terex scraper made by the Terex Earth Moving Equipment Division of General Motors Corporation. In any event, the scraper 14 comprises a suitable frame 16 which typically terminates in a rearwardly extending projection 18 which forms the rear end 12 of the scraper 14, to which the usual fixed bumper plate (not shown) is suitably applied.

The cushioned bumper 10 generally comprises a housing 20 having a base plate 22 closing one end 24 of same, with the other end 26 being open as at 28 to receive a plunger structure 30 which has one end 32 of same directed towards the base plate 22 and the other end 34 equipped with a suitable bumper plate structure 36.

Interposed between the plunger structure 30 and the housing 20 is hydraulic cushioning unit (see FIGS. 3 and 4) which is of the pressure sensitive variable orifice metering type, and, in the embodiment illustrated, a pair of resilient cushions 42 disposed onv either side of the hydraulic cushioning unit.

The end 32 of the plunger structure 30 seats against the base plate 22 to define the fully contracted relation of the bumper, and the plunger structure 30 carries on either side of same a lug 44, which lugs 44 respectively cooperate with the special built up lug plates 46 applied to either side of the housing to define the extended relation of the bumper, under the biasing action of return springs 48 and 50.

As disclosed in said Peterson application, a scraper 14 that is stalled is brought into movement by a bulldozer impacting into the bumper plate 36 of the cushion bumper 10 at a speed on the order of l to 2 miles per hour, with the bumper following the reaction curve that is generally simulated in the drawings of said application. The force travel involved is initially substantially horizontally, and thus is substantially of the constant force travel, and then slowly rises to about the l0,000 lb. reaction force level at approximately the three-quarter point of the stroke length, at which point reaction force smoothly curves upwardly to about the 80,000 lb. level at the end of the stroke.

In this connection, the hydraulic cushioning device 40 allows a safety factor, represented by the bulge in the force travel curve shown in said application, in the event that the scraper when being pushed by the bulldozer through the bumper 10 strikes an immovable object such as a boulder. After the initial shock of striking such an object is past, the reaction force curve returns substantially to its design level for completion of the cushioning stroke.

The overall result is that neither the equipment or the operators are subjected to undue impact shocks even though the bulldozer can run into the bumper at speeds on the order of one to two miles per hour to get the stalled scraper into motion.

As more specifically disclosed in said application, the housing 20 in addition to base plate 22 generally comprises top and bottom plates 60 and 62 and side plates 64, fixed together as by welding, to define a guideway 68, of generally quadrilateral transverse cross-sectional configuration (rectangular in the illustrated embodiment, see FIG. 4), for the plunger structure 30, which is similarly contoured. The base plate 22 is fixed, in the illustrated embodiment, to the standard fixed buffer mounting plate (see FIG. 3) that forms a part of the scraper frame 16, as by employing suitable bolts 72.

Side walls 64 are each formed with a slot 74, extending longitudinally of the housing side wall 64, and from their forward edges 76, in which the respective lugs 44 of the plunger structure operate.

Applied over each slot 74, as by employing suitable bolts 78, is the lug plate 46, which has fixed to the forward edge 82 of same, along the inside surface 84 of the respective plates 46, a lug structure 86 with which the lugs 44 respectively cooperate with (see FIG. 3). The lug structure 86 in the form shown comprises a plate 90 having its center open as at 92 (see FIG. 2) about which the plate 90 is welded to the plate 46 where indicated at 94. The plate 90 is also welded to plate 46 as at 96, at the front edge 82 of the plate 46.

As indicated in FIGS. 3 and 4, the side edges 98 of the lugs 44 respectively engage the side edges 100 of the respective lug fonning plates 90, under the biasing action of return springs 48 and 50.

Lug plates 46 are each formed with vent openings 103 for self cleaning purposes. Side walls 64 have suitable wear plates 101 applied to their inner sides 103.

Reinforcing webs 106 are suitably affixed between the laterally extending ends 108 of the base plate 22 and the respective plates 64, as by welding, and above and below the slots 74. Fixed across top plate 60 is brace plate 109 that provides reinforcement necessary when the bulldozer lifts up on the outer end of the plunger when pushing.

The plunger structure 30 comprises in the form shown the bumper plate structure 36 affixed by welding to top and bottom plates 112 and 114 and side plates 116. The contact face defined by plate structure 36 is such that the buffer plate structure 36 presents the generally frusto-pyramidic contour indicated in the drawings, to avoid presenting right angled corners for engagement by the bulldozer blade.

The lugs 44 each comprise a metal block 132 suitably affixed to the respective plunger structure side plates 116, as by welding at 134.

The hydraulic cushioning unit 40 and the resilient cushions 42 are fully disclosed in said application, to which reference may be made for details. In the form shown, the cushioning unit 40 comprises ram having end plate 146 seated against plunger front plate structure 36, and having its other end (not shown) formed for application within hydraulic cylinder 150.

Cylinder 150 at its end 152 seats against the housing structure base wall 22, and at its other end 154 is equipped with an annular cylinder head member (not which has its other end (not shown) suitably secured to the ram 140, as described in said application, whereby the boot 160 forms a non-sliding seal between the cylinder head and the ram.

Return spring 50 is received about the ram 140 and boot 160, and is interposed between the ram end plate 146 and the end 154 of the hydraulic cylinder 150. Return spring 48 is received in concentric relation about the spring 50, and between the plunger structure front plate 36, and spring seat 151 that is fixed to base plate 22.

The resilient spring devices 42 each comprise a stud 210 suitably fixed to the housing base plate 22, as by welding, and receiving over same annular pad 212 and an impact plate 216 that is also annular in nature. The pad 212 may be formed from butyl rubber, a suitable polyurethane, or the like, and is intended to be of resiliently compressible material that compresses in rubber spring-like manner on being stressed, and which restores itself to its original configuration on being released.

Each resilient spring 42 further includes a pressure plate 218 that is fixed to the plunger structure top, bottom and side plates, as by welding, and is formed with central opening 220 that receives the stud 210, as indicated in FIG. 3.

In the form shown, the plunger structure 30 has a travel stroke extending from the extended position of FIG. 3 to a retracted position in which the end 226 of the plunger structure engages the surface 224 of base plate 22 though this only occurs in practice wherein extremely heavy long duration impacts are occasioned. In one successful embodiment of the invention, this stroke is 4% inches, with the hydraulic cushion 40 having a stroke of 3% inches prior to the engagement of the impact plates 218 with the pad plates 216, after which the resilient cushions 42 act in parallel with the hydraulic cushion to complete the cushioning stroke. The resilient cushions 42 are designed to preclude metal to metal contact within the bumper.

The operation of the cushioning unit 40 and cushions 42 is the same as described in said application.

In the form shown, suitable reinforcing plates 250 are fixed between the upper and lower housing plates and the scraper frame 16. The plates 250 are formed with openings 252 to receive chains applied to a jack device of a suitable type, for securing the respective upper plates 250 to the respective lower plates 250, across the buffer plate 36, with the jack device seated against plate structure 36, whereby compression of the plunger structure inwardly of the housing may be effected against the action of biasing springs 48 and 50 for purposes of disconnecting the plates 46 from housing side plates 64 to disassemble the bumper.

Ordinarily, it is the lower side of the bumper plate structure 36 that is engaged by the bulldozer blade, and the upper side of same can be brought into use by removing the plunger structure and turning it upside down, and then reapplying same. The relation of the plunger structure and housing, as well as the manner of fixing the housing to the scraper frame, permit the bulldozer blade to apply a lifting action on the bumper, as well as a pushing action.

In accordance with this invention, the housing has affixed to either side of its open end 26 a pair of U- shaped reinforcing or retainer members 270 that are formed from bar stock and that define end or leg portions 272 and 274 (see FIG. 4) that are respectively fixed to the housing, and a main body portion 276 that spans the respective side plates 64 and is spaced outwardly therefrom to receive the respective lug plates 46 on either side of the housing 20 (see FIG. 3). The main body portions 276 of the respective members 270 abut the end edge portions 278 of the respective webs 106 on either side of the housing 20.

In the form shown, the ends 272 of the respective members 270 are affixed, as by welding at 280, to the brace plate 109, which in turn is suitably affixed to the housing top plate 60 as by welding, and the end or leg portion 274 is affixed to the housing bottom plate as by welding at 282 and 284. The main body portion 276 is affixed to the respective edge portions 278 of the respective webs 106 as by welding at 288 and 290.

In addition, the respective lug plates 46 are each provided with a stop lug 292, affixed thereto as by welding, which lugs 292 are located on the respective lug plates 46 in substantial abutting relation with the respective side surfaces 294 of the respective members 270 (see FIG. 3).

The result is that on recoil of the plunger 36 such that its lugs 44 engage lug structures 86 of the respective lug plates 46, the members 270 restrain the tendency of the lug plates 46, to twist outwardly of the housing, which would tend to pop off the heads of bolts 78 and exert destructive forces on the welded joints between the top, bottom and side plates along the side edges of housing 20.

In addition, stop lug 292 is urged against the face 294 of the respective retainer or reinforcing members 270, on either side of the housing, to take up the recoil forces involved, thereby relieving the bolts 78 from subjection to such forces.

This permits the bolts 78 to be reduced to four in number for each lug plate 46, as indicated in the drawmgs.

The lug plates 46, as modified in accordance with the invention, may be removed for repair or replacement by retracting the plunger structure 36 against the action of its biasing springs 48 and 50 (as by employing the means previously described), a distance to permit the lug plates 46 to be moved in the direction of the housing base plate, on removal of the bolts 78, sufficiently to permit the edge 82 of the respective lug plates to pass through the space between the respective members 270 and the housing side plates, whereupon the respective lug plates may be readily removed from the housing. Reapplication is in a reverse manner.

The result is that on recoil of the plunger structure against the lug structure 86 carried by the lug plates 46, the open end of the housing 20 is held against forces tending to open same up along the weld joints at its side edges, and the recoil forces are rigidly backed up independently of the fastener bolts 78. The purpose of the bolts 78 is now reduced to mounting the respective lug plates on the housing side plates.

The foregoing description and the drawings are given merely to explain and illustrate the invention and the invention is not to be limited thereto, except insofar as the appended claims are so limited, since those skilled in the art who have the disclosure before them will be able to make modifications and variations therein without departing from the scope of the invention.

I claim:

1. In a cushioned bumper for scrapers that includes an open ended housing, a cushioned plunger structure reciprocably mounted in said housing for movement longitudinally thereof for a stroke of predetermined length, with said plunger structure projecting exteriorly of said housing through the housing open end and carrying a buffer plate structure, means for resiliently biasing the plunger structure outwardly of the open end of said housing, and stop means limiting movement of said plunger structure exteriorly of said housing; the improvement wherein:

said stop means comprises a pair of stop lugs fixed to said plunger structure and disposed on either side of same,

and a pair of internal stop lugs fixed to said housing and disposed on either side of said plunger structure for engagement by the respective plunger structure lugs.

said internal stop lugs defining stop faces adapted to be engaged by the respective plunger structure lugs,

and means for restraining said housing lugs against displacement laterally outwardly of the housing on engagement of said plunger structure lugs with said housing lugs,

said restraining means comprising:

a retainer member for each housing lug,

said retainer members each comprising:

a rigid element disposed in lateral alignment with the respective housing lugs exteriorly of said housing and in lateral movement restraining relation thereto,

said elements having their respective ends fixed to said housing,

said housing having a pair of external stop lugs affixed thereto and respectively disposed adjacent the respective internal stop lugs thereof and in substantial abutting relation with the respective rigid elements on the sides thereof corresponding to the location on the respective internal stop lugs of their respective stop faces.

2. In a cushioned bumper for scrapers that includes an open ended housing of quadrilateral transverse cross-sectional configuration, a cushioned plunger structure reciprocably mounted in said housing for movement longitudinally thereof for a stroke of predetermined length, with said plunger structure projecting exteriorly of said housing through the housing open end and carrying a buffer plate structure, means for resiliently biasing the plunger structure outwardly of the open end of said housing, and stop means limiting movement of said plunger structure exteriorly of said housing; the improvement wherein:

said stop means comprises a pair of stop lugs fixed to said plunger structure and disposed on either side of same,

and a pair of internal stop lugs fixed to said housing on oppositely disposed walls thereof and disposed on either side of said plunger structure for engagement by the respective plunger structure lugs,

said internal stop lugs defining stop faces adapted to be engaged by the respective plunger structure lugs,

and means for restraining said housing lugs against displacement laterally outwardly of the housing on engagement of said plunger structure lugs with said faces of said housing lugs,

said restraining means comprising:

a retainer member for each housing lug,

a rigid stiffener element having a holder portion disposed in lateral alignment with the respective housing lugs exteriorly of said housing and in lateral externally directed movement restraining relation thereto,

said elements having end portions on either side of their respective holder portions, with said ends being fixed to said housing,

said housing having a pair of external stop lugs affixed thereto and respectively disposed adjacent the respective internal stop lugs thereof and in substantial abutting relation with the respective holder portions of respective stiffener elements, on the sides thereof corresponding to the location on the respective internal stop lugs of their respective stop faces.

3. The improvement set forth in claim 2 wherein:

said housings walls are slotted longitudinally of said housing and said plunger structure stop lugs are respectively received in the respective housing slots,

said housing stop lugs each being fixed to a mounting plate made fast to the respective housing walls over the respective slots,

with the respective mounting plates having the portion of same to which the respective internal lugs are affixed disposed between the respective stiffener holder portions and said plunger structure.

4. The improvement set forth in claim 3 wherein:

said housing external stop lugs are respectively affixed to the respective mounting plates.

5. The improvement set forth in claim 3 including:

spaced stiffener plates fixed to each of said housing walls and extending longitudinally thereof,

said stiffener elements being respectively made fast to the respective stiffener plates of the respective walls thereof.

6. The improvement set forth in claim 3 wherein:

said housing is formed by top, bottom and side plates, with said side plates respectively forming said walls thereof,

said stiffener elements having their respective end portion made fast to the housing top and bottom plates respectively.

7. The improvement set forth in claim 6 wherein:

said stiffener elements are U-shaped in configuration with the holder portions thereof uniformly spaced from said housing walls.

8. The improvement set forth in claim 6 wherein:

said mounting plates are respectively fixed to said housing side walls by upper and lower pairs of mounting bolts. 

1. In a cushioned bumper for scrapers that includes an open ended housing, a cushioned plunger structure reciprocably mounted in said housing for movement longitudinally thereof for a stroke of predetermined length, with said plunger structure projecting exteriorly of said housing through the housing open end and carrying a buffer plate structure, means for resiliently biasing the plunger structure outwardly of the open end of said housing, and stop means limiting movement of said plunger structure exteriorly of said housing; the improvement wherein: said stop means comprises a pair of stop lugs fixed to said plunger structure and disposed on either side of same, and a pair of internal stop lugs fixed to said housing and disposed on either side of said plunger structure for engagement by the respective plunger structure lugs. said internal stop lugs defining stop faces adapted to be engaged by the respective plunger structure lugs, and means for restraining said housing lugs against displacement laterally outwardly of the housing on engagement of said plunger structure lugs with said housing lugs, said restraining means comprising: a retainer member for each housing lug, said retainer members each comprising: a rigid element disposed in lateral alignment with the respective housing lugs exteriorly of said housing and in lateral movement restraining relation thereto, said elements having their respective ends fixed to said housing, said housing having a pair of external stop lugs affixed thereto and respectively disposed adjacent the respective internal stop lugs thereof and in substantial abutting relation with the respective rigid elements on the sides thereof corresponding to the location on the respective internal stop lugs of their respective stop faces.
 2. In a cushioned bumper for scrapers that includes an open ended housing of quadrilateral transverse cross-sectional configuration, a cushioned plunger structure reciprocably mounted in said housing for movement longitudinally thereof for a stroke of predetermined length, with said pluNger structure projecting exteriorly of said housing through the housing open end and carrying a buffer plate structure, means for resiliently biasing the plunger structure outwardly of the open end of said housing, and stop means limiting movement of said plunger structure exteriorly of said housing; the improvement wherein: said stop means comprises a pair of stop lugs fixed to said plunger structure and disposed on either side of same, and a pair of internal stop lugs fixed to said housing on oppositely disposed walls thereof and disposed on either side of said plunger structure for engagement by the respective plunger structure lugs, said internal stop lugs defining stop faces adapted to be engaged by the respective plunger structure lugs, and means for restraining said housing lugs against displacement laterally outwardly of the housing on engagement of said plunger structure lugs with said faces of said housing lugs, said restraining means comprising: a retainer member for each housing lug, a rigid stiffener element having a holder portion disposed in lateral alignment with the respective housing lugs exteriorly of said housing and in lateral externally directed movement restraining relation thereto, said elements having end portions on either side of their respective holder portions, with said ends being fixed to said housing, said housing having a pair of external stop lugs affixed thereto and respectively disposed adjacent the respective internal stop lugs thereof and in substantial abutting relation with the respective holder portions of respective stiffener elements, on the sides thereof corresponding to the location on the respective internal stop lugs of their respective stop faces.
 3. The improvement set forth in claim 2 wherein: said housings walls are slotted longitudinally of said housing and said plunger structure stop lugs are respectively received in the respective housing slots, said housing stop lugs each being fixed to a mounting plate made fast to the respective housing walls over the respective slots, with the respective mounting plates having the portion of same to which the respective internal lugs are affixed disposed between the respective stiffener holder portions and said plunger structure.
 4. The improvement set forth in claim 3 wherein: said housing external stop lugs are respectively affixed to the respective mounting plates.
 5. The improvement set forth in claim 3 including: spaced stiffener plates fixed to each of said housing walls and extending longitudinally thereof, said stiffener elements being respectively made fast to the respective stiffener plates of the respective walls thereof.
 6. The improvement set forth in claim 3 wherein: said housing is formed by top, bottom and side plates, with said side plates respectively forming said walls thereof, said stiffener elements having their respective end portion made fast to the housing top and bottom plates respectively.
 7. The improvement set forth in claim 6 wherein: said stiffener elements are U-shaped in configuration with the holder portions thereof uniformly spaced from said housing walls.
 8. The improvement set forth in claim 6 wherein: said mounting plates are respectively fixed to said housing side walls by upper and lower pairs of mounting bolts. 